Method of producing metals and metal alloys

ABSTRACT

A method and an apparatus for producing metals and metal alloys from metal oxides in a metallurgical vessel containing a molten bath having a metal layer and a slag layer is disclosed. The method is characterized by injecting a carrier gas and a solid carbonaceous material and/or metal oxides into the molten bath from a side of the vessel that is in contact with the molten bath or from above the molten bath so that the solids penetrate the molten bath and cause molten metal to be projected into the gas space above the molten bath to form a transition zone. The method is also characterized by injecting an oxygen-containing gas into the gas space to post-combust reaction gases released from the molten bath into the transition zone.

FIELD OF THE INVENTION

The present invention relates to a method of producing metals and metalalloys, in particular although by no means exclusively iron and ironalloys, from metal oxides, such as ores and partly reduced ores, in ametallurgical vessel containing a molten bath.

BACKGROUND OF THE INVENTION

A known method of producing molten iron from iron ore is describedgenerally as the HIsmelt Process and is based on forming a bath ofmolten iron and slag in a smelt reduction vessel which comprises:

i. bottom tuyeres for injecting solid carbonaceous material and acarrier gas into the molten bath;

ii. top tuyeres for injecting iron ore, which may be pre-heated and/orpartially reduced iron ore, into the molten bath from above the surfaceof the molten bath; and

iii. top tuyeres for injecting air into the space above the surface ofthe molten bath to after-burn or post-combust reaction gases, such as COand H₂, released from the molten bath.

In accordance with the HIsmelt Process, the carbonaceous material actsas a reductant and an energy source.

An important feature of the HIsmelt Process is to form a transition zonein the gas space above the molten bath surface in which there areascending and thereafter descending droplets or splashes of molten metaland slag which mix with reaction gases from the molten bath, top blownhot air, and the reaction gases from afterburning. The purpose of thetransition zone is to facilitate the transfer to the molten bath of heatthat is released by afterburning reaction gases from the molten bath. Inaccordance with the HIsmelt Process, the transition zone is formed byvigorous bottom injection of carbonaceous material and carrier gas intothe molten bath which causes droplets and splashes of molten metal andslag to be projected from the molten bath.

A recent development of the HIsmelt Process is described in Australianpatent application 48938/93 entitled "A Method for Intensifying theReactions in Metallurgical Reaction Vessels" in the name ofTechnological Resources Pty Limited. The Australian patent applicationclaims a priority date of Oct. 16, 1992 from German patent application4234974.

The Australian patent application describes that an improvement in heattransfer efficiency of the HIsmelt Process can be obtained bycontrolling the bottom injection of carbonaceous material and carriergas so that the transition zone is defined by a "fountain" of splashesand droplets of molten iron and slag. The paragraph bridging pages 5 and6 of the patent specification of the Australian patent applicationdescribes that:

"The invention is also based on the finding that the reactions inmetallurgical reaction vessels are increased if fractions of the smeltare ejected from the bath like a fountain through the amount of gasintroduced via the under-bath tuyeres and these fractions of the smeltmove within the gas space in the form of drops, splashes and largeparticles of the smelt on ballistic trajectories that are only stoppedwhen the smelt fractions hit the vessel wall or the smelt itself,collide with other smelt fractions or are drawn in by the oxidisinggases blown onto the bath in the form of free jets."

An object of the present invention is to provide an alternative methodof generating a fountain-like transition zone.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method ofproducing metals and metal alloys from metal oxides in a metallurgicalvessel containing a molten bath, the molten bath comprising a metallayer and a slag layer on the metal layer, the method beingcharacterised by the steps of:

i. injecting a carrier gas and solid carbonaceous material and/or metaloxides and/or other solid material into the molten bath through asection of a side of the vessel that is in contact with the molten bathand/or from above the molten bath so that the carrier gas and solidcarbonaceous material and/or metal oxides and/or other solid materialcause molten metal to be projected into a space above the surface of themolten bath to form a transition zone; and

ii. injecting an oxygen-containing gas into the space above the moltenbath surface to afterburn reaction gases released from the molten bathinto the transition zone.

The term "transition zone" is understood herein to mean a zone above themolten bath in which there are ascending and thereafter descendingdroplets or splashes of molten metal.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the realisation that it is possible toform the transition zone of the HIsmelt Process, without loss ofperformance and with engineering advantages, by injecting carrier gasand carbonaceous material and/or metal oxides and/or other solidmaterial into a molten bath through a section of a side of ametallurgical vessel that contacts the molten bath and/or from above thesurface of the molten bath.

As a consequence, the present invention makes it possible to avoid usingbottom injection of carbonaceous material and carrier gas to form thetransition zone and the engineering difficulties associated with suchbottom injection. One engineering difficulty is that the use of bottomtuyeres makes it necessary to mount the metallurgical vessel forrotation about an axis so that the bottom tuyeres can be rotated clearof the molten bath at turn-down. Furthermore, if bottom tuyeres areeliminated, a much simpler, and more robust, furnace bottom constructionis possible.

The present invention is also based on the realisation that, insituations where step (i) includes injecting carbonaceous material,injection through a tuyere as proposed is an effective means ofachieving the desirable objective of ensuring that carbonaceous materialpenetrates the molten bath, and in particular the metal layer of themolten bath.

It is preferred that step (i) comprises injecting the carrier gas andcarbonaceous material and/or metal oxides and/or other solid materialthrough the side section of the vessel or from above the surface of themolten bath with sufficient momentum to penetrate the molten bath andcause molten metal to be projected into the space above the molten bathsurface to form the transition zone.

It is preferred that step (i) comprises injecting the carrier gas andcarbonaceous material and/or metal oxides and/or other solid materialinto the molten bath to cause molten metal to be projected into thespace above the molten bath surface in a fountain-like manner.

The carbonaceous material may be any suitable carbonaceous material, insolid, liquid or gaseous form.

The metal oxides may be in any suitable form. For example, the metaloxides may be in the form of ores and/or partly reduced ores. The degreeof pre-reduction of the ores may range from relatively low (eg to FeO)to relatively high (70-90% metallisation).

The metal oxides may be pre-heated.

The other solid material may be any suitable material, such as, by wayof example, fluxes or slag forming agents.

The carrier gas may be any suitable carrier gas.

It is preferred that the carrier gas be an oxygen-deficient gas.

It is preferred that the carrier gas comprise nitrogen.

The carrier gas may comprise waste process gas released from the vesselwhich has been used, by way of example, to partially reduce metal oxidesthat subsequently are transferred to the vessel.

The oxygen-containing gas may be any suitable gas such as, but notlimited to, air or oxygen enriched air.

It is preferred that the oxygen-containing gas be air.

It is preferred particularly that the air be preheated.

According to the present invention there is also provided an apparatusfor producing metals and metal alloys from metal oxides comprising:

i. a metallurgical vessel for containing a molten bath, the vesselhaving a base, a side wall, a roof, and a gas outlet;

ii. a first tuyere for injecting an oxygen-containing gas into a spacein the vessel above the molten bath; and

iii. a second tuyere above the molten bath or in a section of the sideof the vessel that is in contact with the molten bath for injecting acarrier gas and solid carbonaceous material and/or metal oxides and/orother solid material into the molten bath to cause molten metal to beprojected into a space above the surface of the molten bath to form atransition zone.

The term "tuyere" is understood herein to include any means forinjecting solids and/or gases into a metallurgical vessel.

An outlet end of the second tuyere may be positioned above the surfaceof the molten bath or may be submerged in the molten bath.

It is preferred particularly that the second tuyere be positioned todirect the carrier gas and carbonaceous material and/or metal oxidesand/or other solid material into the molten bath so that the carrier gasand carbonaceous material and/or metal oxides and/or other solidmaterial can cause molten metal and slag in the molten bath to beprojected from the molten bath in a fountain-like manner.

The tuyeres may be any suitable configuration.

It is preferred, although by no means essential, that the tuyeres bewater-cooled.

The present invention is described further by way of example withreference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section through one embodiment of a metallurgicalvessel in accordance with the present invention for carrying out anembodiment of the method of the present invention; and

FIG. 2 is a vertical section through another embodiment of ametallurgical vessel in accordance with the present invention forcarrying out the embodiment of the method of the present invention.

DETAILED DISCUSSION OF THE DRAWINGS

The following description is in the context of smelting iron ore toproduce molten iron and it is understood that the present invention isnot limited to this application and is applicable to any suitablemetallic ores and/or concentrates.

The figures illustrate, albeit in simplified, schematic form, twoembodiments of a wide range of possible embodiments of an apparatus forsmelting iron ore in accordance with the present invention.

With reference to the figures, each apparatus comprises a metallurgicalvessel 3 having a metal shell and a lining of refractory material whichis adapted to retain a bath 9 of molten iron and slag. Each vessel 3comprises a bottom 4, a cylindrical side wall 6, a roof 20, and a gasoutlet 8.

The apparatus in FIG. 1 comprises a single tuyere 5 in the side wall 6of the vessel 3 which is arranged to extend into the vessel 3 to aposition at which, in use, the open end of the tuyere 5 is a shortdistance above the surface of the molten bath 9. The apparatus in FIG. 2comprises two diametrically opposed tuyeres 5 in the side wall 6 of thevessel 3. In this embodiment, the open ends of the tuyeres 5 aresubstantially flush with the inner surface of the side wall 6. As withthe arrangement shown in FIG. 1, the open ends of the tuyeres are ashort distance above the surface of the molten bath 9. It is noted thatthis is not an essential feature of the present invention, and the openends may be submerged in the molten bath 9.

In both embodiments, the tuyeres 5 are angled downwardly toward thesurface of the molten bath 9.

With further reference to the figures, each apparatus further comprisesa tuyere 10 extending generally vertically into the vessel 3 through theroof 20.

In accordance with an embodiment of the method of the present invention,the operating conditions are selected so that coal and iron ore areentrained in a suitable carrier gas, such as nitrogen, and are injectedthrough the tuyere(s) 5 into the molten bath 9 containing molten ironand slag with sufficient momentum to penetrate the molten bath 9 and tocause splashes and droplets of molten iron and slag to be projectedupwardly from the surface of the molten bath 9 in a fountain-like mannerto form a transition zone 11 in a space 14 in the vessel 3 above themolten bath surface.

Further, a suitable oxygen-containing gas, such as hot air or oxygenenriched air, is injected via the top tuyere 10 into the vessel 3 forthe purpose of afterburning reaction gases, such as CO and H₂ that arereleased from the molten bath 9 into the space 14 and otherwise would bedischarged from the vessel 3 via the gas outlet 8.

There are number of factors that affect the formation of the transitionzone 11 and these include, by way of example:

i. the diameter of the tuyere(s) 5;

ii. the position (including the angle) of the tuyere(s) 5 with respectto the surface of the molten bath 9;

iii. the momentum of the stream of coal/ore/carrier gas/other solidmaterial injected through the tuyere(s) 5; and

iv. the number of the tuyere(s) 5 and the size of the vessel 3.

With regard to item (ii), in the context of the preferred embodimentshown in FIGS. 1 and 2, the tuyere(s) 5 may be located in the side wall6 of the vessel 3 at any position above or below a suitable referencesurface of the molten metal bath 9 provided that the angle of injectionand the other factors noted above are such that the stream(s) ofcoal/ore/carrier gas injected, in use, through the tuyere(s) 5 canpenetrate the molten bath 9 as required to cause splashes and dropletsof molten iron and slag to be projected from the molten bath 9 to formas a fountain to form the transition zone 11. One suitable referencesurface may be the quiescent level of the molten bath 9, i.e. the levelof the molten bath prior to injection of materials into the vessel 3.Whilst not wishing to be limited to any specific dimensions, typically,the open end(s) of the side tuyere(s) 5 may be in the range of 0.5meters above to 0.5 meters below the reference surface of the moltenbath 9.

With regard to item (iii), the momentum of the stream ofcoal/ore/carrier gas injected through the tuyere(s) 5 is dependent on anumber of factors including, but not limited to, the velocity of thestream, the solids loading of the stream, and the required size of thetransition zone 11.

In any given situation, an optimum set of operating conditions can bedetermined by consideration of the above (and other relevant) factors.

As is discussed above, it is believed by the applicant that the methodand apparatus of the present invention make it possible to simplify theengineering associated with bath smelting processes where after-burningis achieved in the gas space above the molten bath, such as the HIsmeltProcess.

In addition, it is believed by the applicant that the method andapparatus of the present invention make it possible to use relativelywide diameter tuyeres 5 which would provide an additional advantage ofthe present invention of minimising the risk of blockage and making itpossible to inject a wider size range of coal and/or ore through thetuyeres 5.

Many modifications may be made to the embodiments of the method and theapparatus described above with reference to the drawings withoutdeparting from the spirit and scope of the present invention.

By way of example, whilst the preferred embodiments described aboveinclude a cylindrical vessel 3, it can readily be appreciated that thepresent invention is not so limited and may be any suitable shape ofpressurised or unpressurised vessel.

Furthermore, whilst the preferred embodiments are based on the use ofcoal/ore/carrier gas to provide sufficient momentum, the presentinvention is not so limited and extends to the separate use of coal orore with a suitable carrier gas.

Furthermore, as indicated previously, whilst the tuyeres 5 of thepreferred embodiments are positioned so that the open ends of thetuyeres 5 are above the surface of the molten bath, the presentinvention is not so limited and extends to arrangements in which theopen ends of tuyeres 5 are submerged in the molten bath 9.

Furthermore, whilst the tuyeres 5 of the preferred embodiments arepositioned in the sides 6 of the vessel 3, the present invention extendsto arrangements in which the tuyeres 5 are arranged to extend into thevessel through the roof 20.

Finally, whilst the tuyere 10 for oxygen-containing gas injection shownin the figures extends through the roof 20 in a generally verticalorientation, the present invention is not so limited and the tuyere 10may be positioned in any suitable location to efficiently after-burnreaction gases released from the molten bath 9.

What is claimed is:
 1. A method of producing metals and metal alloysfrom metal oxides in a metallurgical vessel containing a molten bath,said vessel comprising a sidewall and a roof, the molten bath comprisinga metal layer and a slag layer on the metal layer, the method beingcharacterized by the steps of:i. injecting a solid material being solidcarbonaceous material and/or metal oxides with a carrier gas through oneor more tuyeres, wherein each tuyere injecting solid material within thevessel extends through the sidewall and is angled downwardly, and theinjected solid material has sufficient momentum so that the solidcarbonaceous material and/or metal oxides and the carrier gas penetratethe molten bath and cause molten metal to be projected into a spaceabove the surface of the molten bath to form a transition zone; and ii.injecting an oxygen-containing gas into the space above the molten bathsurface to afterburn reaction gases released from the molten bath intothe transition zone.
 2. The method defined in claim 1 wherein step (i)comprises injecting the carbonaceous material only with sufficientmomentum to penetrate the metal layer.
 3. The method defined in claim 1or claim 2 wherein the molten metal is projected into the space abovethe molten bath surface in a fountain-like manner.
 4. The method definedin claim 1 wherein the metal oxides are in the form of ores and/orpartly reduced ores.
 5. The method defined in claim 1 wherein the metaloxides are pre-heated.
 6. The method defined in claim 1 wherein theoxygen-containing gas is preheated air.
 7. The method defined in claim 1wherein step (i) comprises injecting the carbonaceous material, metaloxides and carrier gas with sufficient momentum to cause molten metaland slag to be projected into the space above the molten bath surface toform the transition zone.
 8. The method defined in claim 7 wherein themolten metal and slag are projected into the space above the molten bathsurface in a fountain-like manner.
 9. The method defined in claim 1wherein step (i) comprises injecting carbonaceous material and metaloxides through the same tuyere or tuyeres.
 10. The method defined inclaim 1 wherein step (i) comprises injecting carbonaceous material andmetal oxides through separate tuyeres.
 11. The method defined in claim 1wherein step (i) further comprises injecting other solid material withthe carrier gas.
 12. The method defined in claim 11 wherein the othersolid material comprises one or more of fluxes or slag forming agents.13. The method defined in claim 1 comprising injecting carbonaceousmaterial and metal oxides with the carrier gas through one or more thanone tuyere that extend within the vessel.
 14. The method defined inclaim 13 comprising injection the carbonaceous material and metal oxideswith the carrier gas through one or more than one tuyere located suchthat an outlet end of each tuyere is submerged in the bath.
 15. Themethod defined in claim 1 wherein the carrier gas is an oxygen-deficientgas.
 16. The method defined in claim 15 wherein the carrier gascomprises nitrogen.
 17. The method defined in claim 15 wherein thecarrier gas comprises waste reaction gas released from the vessel whichhas been used to partially reduce metal oxides that subsequently aretransferred to the vessel.